new ported helper classes for the Formula Editor
Formula tokens an test cases
keyboard draft
added exp to functions
bugfixes

bugfix for inverse trigonometric functions and enum to string functions
added FormulaTest and Formula init functions
new helper classes for formula-editor (intern)
finished InternFormula
integrated first functionality to controller
Merge pull request #370 from Catrobat/formula-editor-mh

added FormulaTest and Formula init functions
Merge branch 'formula-editor-christian' into formula-editor

Conflicts:
	src/Catty.xcodeproj/project.pbxproj
	src/Catty/Formula.m
Merged branches from Christian and Michael
display formula for Bricks at the "Scripts" view
added extern function name conversation
Merge branch 'formula-editor-christian' into formula-editor

Conflicts:
	src/Catty/FormulaEditor.xib
change formulas + "Edit Formula" context menu

+ added click event for every formula
+ open formula editor when clicked on “Edit Formula” in context menu
+ display “Edit Formula” in context menu only when brick has formula
+ bugfixes for BrickCell context menu
Merge pull request #374 from Catrobat/formula-editor-michael

+ onclick event for every formula
+ open edit when clicked on "Edit Formula" context menu
+ bugfixes
saves and updates formula in BrickCell
Merge pull request #375 from Catrobat/formula-editor-michael

saves and updates formula in BrickCell
added FormulaEditorHistory class